[backend] Fix No error when merging two entities with a higher confidence level (#6502)

[SarahBocognano]

Proposed changes

• Remove the filter that was implemented before in the background task to avoid error. We want to display an error now
• Move the check of confidence low level in middleware (mergeEntities) instead of the function that compute the list task

Related issues

• No error when merging two entities with a higher confidence level #6502
• The merge does not take into account the max confidence level in some cases. #6501

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 68.58%. Comparing base (cff70c3) to head (ecc10b8).
Report is 8 commits behind head on master.

Files	Patch %	Lines
...tform/opencti-graphql/src/domain/backgroundTask.js	33.33%	2 Missing ⚠️
...latform/opencti-graphql/src/manager/taskManager.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6565      +/-   ##
==========================================
+ Coverage   67.76%   68.58%   +0.81%     
==========================================
  Files         532      532              
  Lines       65069    65048      -21     
  Branches     5464     5964     +500     
==========================================
+ Hits        44097    44613     +516     
+ Misses      20972    20435     -537     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.